I would suggest that the ASI should only be part of the equation. You need
to know the correct attitude (with reference to the horizon) that gives a
safe approach speed. If you fly with reference to the ASI alone you end up
chasing the airspeed and worse still have your eyeball inside the cockpit
instead of keeping an eye on the attitude and where you are heading.
On my first ever solo (in a glider) the ASI failed completely and I had to
fly the circuit and land without any speed reference whatsoever. Fortunately
I was taught to fly by attitude and coped with what would have otherwise
been a nasty situation.
If your airspeed indicator were to fail would you know what attitude to fly
to land safely. If you dont recognise what attitude gives a safe flying
speed (flaps up and flaps down) would you be able to cope with such an
emergency.
----- Original Message -----
Sent: Wednesday, August 02, 2006 3:13 PM
>
>
> I don't see the ASI and the AOA as entirely different things, especialy
> in a small GA cockpit. The ASI can be calibrated to read angles instead
> of speed based on aircraft weight, like the movable outer ring that is
> used for calibrating TAS based on temperature. A true AOA independent
> of weight is useful only in large transport aircraft where the weight
> could vary significantly.
>
>
> --- Mark Burton <markb@ordern.com> wrote:
>
>>
>> Folks,
>>
>>
>> graham@gflight.f9.co.u wrote:
>> >
>> > Mike will have a much more valid opinion than me but I believe the
>> > sensible way to monitor airspeed is by angle of attack, the
>> instrument
>> > tells that that your airspeed is going to change, you can correct
>> the
>> > changed AoA instantly and speed won't change The ASI tells you at
>> least
>> > 20 seconds after it's changed which means you then have to regain
>> > momentum which will take another 20 seconds or more. Another
>> advantage
>> > that correct AoA is not dependant on weight, so the figure for
>> stall,
>> > cruise max range etc all remain constant.
>> > my 2 cents
>> > Graham
>> >
>>
>>
>> There is much good information in Graham's message but I feel that
>> this last paragraph is misleading. Unless your ASI is particularly
>> sluggish, it will indicate changes in airspeed almost instantly (i.e.
>> not 20 seconds later). What takes the time is actually changing the
>> speed of the aircraft relative to the surrounding air. Fitting an
>> AoA gauge does not make your aircraft accelerate any quicker!
>>
>> Let's imagine the situation where you are on approach and your
>> airspeed is a little below the optimum speed (the AoA is higher than
>> desired). Assuming you are not too low, you lower the nose to
>> increase the speed (and reduce the AoA). As soon as the nose is
>> lowered, the AoA will decrease and if you have an AoA gauge that will
>> be indicated immediately. The airspeed, however, does not change
>> straightaway (the ASI lag!!!) After a while, your airspeed will
>> settle at the new increased value. (perhaps a kind aerodynamics
>> person can provide us with a succinct description of what causes the
>> airspeed to increase when the AoA is reduced).
>>
>> Moving the stick forward to reduce the AoA is the crucial action.
>> Having moved the stick, the pilot then has to wait until the speed
>> stabilises before sampling the ASI again (all gliding instructors
>> will remember giving this demo). If the speed doesn't have to change
>> by very much (say, < 5 kts) then the pilot doesn't have to wait very
>> long (certainly less than 20S).
>>
>> The rational behind the talking ASI is that if the airspeed on
>> approach is not far from the desired speed, then the pitch/throttle
>> adjustments required to return to that speed are small and the time
>> lag between making an adjustment and achieving the desired speed is
>> small. The pilot is "nagged" into maintaining the correct airspeed
>> through small changes in pitch/power.
>>
>> By nagging the pilot to maintain a sensible speed, the talking ASI
>> not only protects against stalling, it helps you obtain the
>> stabilised approach that Mike Parkin enthused about and is so
>> important when operating out of small fields.
>>
>> I understand the benefits of flying by AoA and if someone produced a
>> low cost, reliable, easy to fit and calibrate, AoA instrument that
>> didn't require you to have your eyes in the cockpit on approach, I
>> would be tempted to have one.
>>
>> Mark
>>
>>
>>
>>
>> Read this topic online here:
>>
>> http://forums.matronics.com/viewtopic.php?p=51717#51717
>>
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